The present invention relates to a method for marking a sintered product with identification information while minimizing the generation of contamination. The present invention also relates to a method for fabricating a substrate for a magnetic head including the marking step, a sintered product with identification information marked thereon, a magnetic head, and a storage medium drive.
In recent years, thin film magnetic heads of various constructions have been used as magnetic head sliders for hard disk drives (HDD), tape storages, floppy disk drives (FDD), and the like. Sintered substrates, made of compositions such as Al2O3xe2x80x94TiC, SiC, and ZrO2, are used for such thin film magnetic heads.
FIG. 1A illustrates a typical thin film magnetic head slider 10. The magnetic head slider 10 has two side rails 11 on the track side thereof facing the surface of a magnetic disk. The surface of the magnetic head slider 10 where the side rails 11 are formed is sometimes called an air bearing surface (ABS). When the magnetic disk is rotated at high speed with a motor or the like, in the state where the side rails 11 of the magnetic head slider 10 lightly press the surface of the magnetic disk under head suspension, a layer of air formed on the surface of the magnetic disk intrudes into a gap under the air bearing surface of the slider 10. This causes the magnetic head slider 10 to be slightly lifted. In this way, the magnetic head slider 10 hovers near the surface of the magnetic disk, to effect recording/reproducing operation.
Thin films 12 are formed on one end face of the magnetic head slider 10 for magnetic interaction with a storage medium such as the magnetic disk. The thin films 12 constitute an electric/magnetic transducer element. On the other end face of the magnetic head slider 10, identification information 13, such as a serial number, is engraved. Methods for engraving the identification information 13 on the sintered substrate are disclosed in Japanese Laid-Open Patent Publication No. 9-81922, No. 10-134317, and No. 11-126311, for example.
The magnetic head slider 10 is obtained in the following manner. A bar 20 as shown in FIG. 1B is cut from a sintered substrate 1 as shown in FIG. 1C, and the bar 20 is divided into a plurality of chips. The positional relationship between the sintered substrate 1 shown in FIG. 1C and the magnetic head slider 10 shown in FIG. 1A is such that an end face 4 of the sintered substrate 1 is parallel with the air bearing surface of the magnetic head slider 10.
As the size of thin film magnetic heads 12 is reduced to cope with the reduction in size and weight of electronic apparatuses, the thickness of the sintered substrate 1 (corresponding to the length L of the magnetic head slider 10) is reduced, and the thickness T of the bar 20 (corresponding to the height of the magnetic head slider 10) is reduced. For example, in a magnetic head slider called a pico-slider, L is about 1.2 mm and T is about 0.3 mm. With such a short magnetic head slider, the size of characters to be engraved thereon should also be made smaller.
A laser marking method is commonly used for engraving (hereinafter, also called xe2x80x9cinscriptionxe2x80x9d and xe2x80x9cmarkingxe2x80x9d) of the identification information 13. According to the laser marking method, the identification information 13 shown in FIGS. 1A and 1B is inscribed on the back surface 3 of the substrate 1 in the wafer state before being divided into the bars 20. Subsequently, various thin films 12 are formed on the opposite surface 2 of the substrate 1.
The conventional laser marking method will be described with reference to FIG. 2. The back surface 3 of the sintered substrate 1 is irradiated with a laser beam 6 converged by a lens 5. An irradiated portion of the substrate 1 is rapidly heated and evaporated, so that a small concave portion or recessed portion is formed on the back surface 3 of the substrate 1. At this time, pieces of the sintered material constituting the substrate 1 scatter. Some of these pieces fall back on the substrate 1. By scanning the back surface 3 of the substrate 1 with the laser beam 6, an arbitrary recess pattern can be formed. Thus, by forming a pattern of alphabets, numerals, barcodes, and the like, various types of identification information can be written at arbitrary positions on the substrate 1.
There are problems associated with the conventional laser marking method. First, debris is generated by the laser light irradiation. This debris often causes contamination in later fabrication process steps, by becoming absorbed and accumulated in inscribed grooves and the like. Second, burrs are generated at edges of the grooves during the laser light irradiation. Therefore, an additional step for removing such burrs is required.
FIG. 3A schematically illustrates the cross-section of the sintered substrate 1 after the substrate 1 has been engraved by the conventional laser marking method. This cross-sectional view was drawn based on a photograph taken with a scanning electron microscope (SEM). Referring to FIG. 3A, a deep concave portion 30 is formed on the surface of the substrate 1 by irradiation with laser light. The depth of the concave portion 30, measured from the back surface of the substrate 1 in the direction shown by the arrow a, is 30 to 50 xcexcm. A convex portion (burr) 31 is formed along the edge of the concave portion 30. The height of the burr 31 measured in the direction shown by the arrow b is of the order of several micrometers. The width of the concave portion 30 is of the order of 20 xcexcm, for example. Hereinafter, the depth of the concave portion is referred to as the xe2x80x9cinscription depthxe2x80x9d, and the height of the raised portion around the concave portion is referred to as the xe2x80x9cedge burr heightxe2x80x9d.
A number of particles 32 attach to the wall of the deep concave portion 30 formed by the laser light irradiation. The particles 32 are not necessarily in the form of particles, but are herein called xe2x80x9cparticlesxe2x80x9d for simplification. In order to remove the particles 32 from the substrate 1, a long-duration cleaning step, such as ultrasonic cleaning, is required after the marking step. Even by this cleaning step, however, it is difficult to remove the particles 32 located deep inside the concave portion 30 to a sufficient degree.
If a large number of particles 32 are generated during the laser marking step, part of the particles 32 may be dispersed in a cleaning solution, and part of the particles 32 in the cleaning solution may possibly re-attach to the surface of the substrate 1 that has not been irradiated with laser light (surface 2). If this re-attachment occurs and an insulating thin film made of amorphous aluminum oxide or the like is deposited on the surface 2 of the substrate 1, the particles 32 may be included in the insulating thin film. The surface of the insulating thin film is smoothed before a magnetic thin film is deposited thereon. Therefore, if the particles 32 exist in the insulating thin film, the insulating thin film may be locally peeled off together with the particles 32, resulting in formation of pinholes in the insulating thin film. Even if formation of pinholes is evaded, the insulating thin film may be substantially thinned in some portions due to the existence of the particles 32. The insulating property of such portions of the insulating thin film is decreased. Such inclusion of the particles in the insulating thin film does not necessarily occur. However, as long as the inscribed portions of the back surface of the substrate serve as a dust source, the yield may be lowered in the subsequent steps, and also the reliability of the final products may be decreased.
In order to improve the production yield of thin film magnetic heads, the quality of the insulating film deposited on the sintered substrate 1 should preferably be improved as much as possible. In order to achieve this, the marking step that is a cause of generation of dust or contamination should desirably be improved to minimize generation of dust. In addition, the resultant magnetic head as a complete component should not generate dust. Since the magnetic head is used in a clean environment, generation of dust will cause a problem.
A method for replacing the above laser marking method has also been proposed, where identification information is written on a sintered substrate by chemical etching. However, by this chemical etching method, also, particles enter a concave portion (groove) formed on the substrate surface if the concave portion is deep, resulting in generation of dust or contamination.
An object of the present invention is to provide a marking method for a sintered product that can reduce the generation of dust and minimize the formation of burrs.
Another object of the present invention is to provide methods for fabricating with high yield a sintered product, a magnetic head substrate, a magnetic head, and a storage medium drive with high quality by executing an inscribing step according to the above marking method.
The marking method for a sintered product of the present invention includes forming a concave portion on the sintered product by irradiating the sintered product with laser light to write identification information on the sintered product, wherein the depth of the concave portion is in a range between 0.1 xcexcm and 5 xcexcm, inclusive.
The method for fabricating a magnetic head substrate of the present invention includes the steps of: (1) writing identification information on a first surface of the magnetic head substrate by the above marking method for a sintered product; and (2) subjecting the magnetic head substrate to ultrasonic cleaning.
In a preferred embodiment, the method further includes the step of forming a thin film on a second surface of the magnetic head substrate after the step of subjecting the substrate to ultrasonic cleaning.
The magnetic head substrate of the present invention is marked with identification information by laser light irradiation, wherein the identification information is constructed of a concave portion having a depth in a range between 0.1 xcexcm and 5 xcexcm, inclusive.
The magnetic head of the present invention is marked with identification information by laser light irradiation, wherein the identification information is constructed of a concave portion having a depth in a range between 0.1 xcexcm and 5 xcexcm, inclusive.
Alternatively, the marking method for a sintered product of the present invention includes the steps of: (1) preparing a sintered product formed of a powder mixture including first powder particles of a first material and second powder particles of a second material having an etching characteristic different from the etching characteristic of the first material; and (2) performing selective etching for a selected portion of a surface of the sintered product, the selective etching including etching the first powder particles with priority over the second power particles, thereby to write identification information on the surface of the sintered product.
In a preferred embodiment, the mean grain diameters of the first powder particles and the second powder particles are in a range between 0.3 xcexcm and 5.0 xcexcm, inclusive.
Preferably, the difference in reflectance between the portion of the surface of the sintered product that has been subjected to the selective etching and a portion that has not been subjected to the selective etching is 15% or more for light having a certain wavelength.
The wavelength is preferably included in a wavelength range for light used for irradiating the sintered product for optically reading the identification information.
Preferably, the plane roughness of the portion of the surface of the sintered product that has not been subjected to the selective etching is 5 nm or less.
Preferably, the mean etching depth of the portion of the surface of the sintered product that has been subjected to the selective etching is in a range between 5 nm and 200 nm, inclusive.
The first material and the second material are preferably compounds selected from the group consisting of aluminum oxide, aluminum nitride, silicon oxide, silicon nitride, zirconium oxide, zirconium nitride, silicon carbide, titanium carbide, titanium oxide, and iron oxide.
Alternatively, the method for fabricating a magnetic head substrate of the present invention includes writing identification information on the sintered product by the above marking method for a sintered product.
The method for fabricating a magnetic head of the present invention includes fabricating a magnetic head, provided with the identification information from the magnetic head substrate fabricated by the above method, for fabricating a magnetic head substrate.
The sintered product of the present invention is formed of a powder mixture including first powder particles of a first material and second powder particles of a second material having an etching characteristic different from an etching characteristic of the first material, wherein the first powder particles are selectively etched with priority over the second power particles in a selected portion of a surface of the sintered product, to write identification information on the surface of the sintered product.
In a preferred embodiment, the mean grain diameters of the first powder particles and the second powder particles are in a range between 0.3 xcexcm and 5.0 xcexcm, inclusive.
Preferably, the difference in reflectance between the portion of the surface of the sintered product that has been etched and a portion that has not been etched is 15% or more for light having a certain wavelength.
The wavelength is preferably included in a wavelength range for light used for irradiating the sintered product for optically reading the identification information.
Preferably, the plane roughness of the portion of the surface of the sintered product that has not been etched is 5 nm or less.
Preferably, the mean etching depth of the portion of the surface of the sintered product that has been etched is in a range of 5 nm and 200 nm, inclusive.
The first material and the second material are preferably compounds selected from the group consisting of aluminum oxide, aluminum nitride, silicon oxide, silicon nitride, zirconium oxide, zirconium nitride, silicon carbide, titanium carbide, titanium oxide, and iron oxide.
Alternatively, the magnetic head substrate of the present invention is formed of the above sintered product.
Alternatively, the magnetic head of the present invention includes: the above magnetic head substrate; and an electric/magnetic transducer element formed on the magnetic head substrate.
The storage medium drive of the present invention includes: the above magnetic head; a storage medium having a magnetic recording film on/from which information is recorded/reproduced via the magnetic head; and a motor for driving the storage medium.